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Blasting for surface mining is a source of potentially damaging ground vibrations. Of particular concern are sites with low- frequency surface waves, those below 5 hz. These vibrations can produce excessive structural response and strains in nearby buildings. A U.S. Bureau of Mines study of one such site found the ground acting as the propagating medium primarily responsible for generating and sustaining these low-frequency waves. The observed waves were consistent with predictive models based on layer thicknesses equal to the depths to abandoned underground mines known to exist in the area. A thick zone of low-velocity glacial till also exists between the blasts and the affected homes. Because some influence was also found from the initiation delay timing, blast designs based on specific timing patterns could be used to reduce the generated vibrations at such sites.